Electronic ore sorting



April 18, 1950 E. H. RosE ETAL ELECTRONIC oRE somme 3 Sheets-Sheet 1 Filed April 25, 1946 INVENTORS Pr/vas 7- /r Fase 777/04 Vir/Nas' .IIIIIJIIJ ...l .flllllllllilllllll||1|II|||||||||IIIIL E. H. ROSE ETAL ELECTRONIC ORE SORTING April 1s, 195o 'o' Sheets-Sheet 2 Filed April 25, 1946 INVENTORS TP/v6.97' f Foss By /rr//a/r.' Pfr/Mrs l l l l APril 1 8 1950 E. H. RosE ETAL 2,504,731

ELECTRONIC oRE soRTING Filed April 25, -194e s shams-sheet s Patented Apr.. 18, 1950 ELECTRONIC ORE SORTING Ernest Herbert Rose and Arthur Ernest Prince, Copper Cliil", Ontario, Canada, assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application April 25, 1946, Serial No. 664,772 In Canada March 23, 1946 3 Claims. 1

The present invention relates to improvements in the art of sorting of materials or articles and, more particularly, to a machine for use in the art of sorting of minerals and ores.

Ore or mineral sorting, as generally practiced heretofore-has been dependent upon some characteristic property, such as the magnetic properties of the material being sorted or the specific gravity, etc., as is well known to the art. Hand sorting with visual detection of values was also used. Since the magnetic method was dependent on the magnetic qualities of the material being sorted, it was not adaptable for the removal of non-magnetic material. For example, tramp manganese steel could not be removed by magnetic forces. Magnetic separation suffers the serious handicap of always working against gravity. This handicap is fatal when dealing with lump ore because the weight generally exceeds the magnetic pull except on ores of extremely high magnetic permeability or on very high grade pieces. A further weakness of magnetic separation methods is the rapid decrease in magnetic pull due to distance from the poles. Doubling the distance from the pole results in reducing the magnetic pull by approximately four times with a given magnetic eld strength. In values-bearing magnetic ore, the larger the pieces the greater the mean distance from the poles will be.

Furthermore, it frequently occurs that even when magnetic material is present it cannot be removed from an ore now stream because of the burden of non-magnetic material intimately associated with the magnetic material. On the other hand, for example in the handling of pentlandite-pyrrhotite ores, material of high values is frequently discarded when using the magnetic method of sorting since pentlandte is recovered in such a process only by its association with magnetic pyrrhotite and thus the ore of highest grade in terms of pyrrhotite-nickel ratio is not recovered.

Another method heretofore commonly employed for concentrating lump ore was by hand sorting on visual appearance. This method had numerous disadvantages. Judgment by visual inspection is neither quick nor delicate. The lumps may be covered with dust or mud and the values hence cloaked against visual detection. Also the value may be concealed within the interior of the ore lump and thus not visually detectable. Finally, hand sorting requires manual handling of all the pieces selected.

Another method of ore separation depends largely on the specific gravity of the material being sorted. The gangue may be made up of constituents of widely diierent gravities, such that recovery of composite lumps of values in light gangue requires the unprofltable recovery of barren and valueless gangue of that gravity which equals the gravity of such composite lumps. Also, other subsequent operations, such as the recovery of the medium, are required.

We have discovered a method for the sorting of value-bearing ores which is entirely independent of gravity and can make much lower tailing assay and which, being an entirely dry process, requires no chemical reagents of any kind and particularly requires no water. Our process is not only highly eillcient in comparison with earlier practice, but is also highly economical since the cost of chemical reagents, the cost of their recovery, and the cost of providing and subsequently removing water are completely eliminated.

Stated broadly, we have discovered that an improved ore sorter can be made by incorporating a conventional inductive electrical bridge circuit which can be readily adapted to the detection of the existence and degree of the electrical energyabsorptive capacity of a wide range of materials, such as ores, by the inclusion of a detecting means in that electrical circuit.

For purposes of illustration, the present invention contemplates the'use of a balanced bridge circuit supplied by an alternating E. M. F. in the audio range 200 to l0 000 cycles per second. This audio frequency power is applied across the arms of a self-inductance bridge, the inductance arms of which may be multiple turn coils of 1000 turns each, 6-inch inside diameter and 2-inch face diameter. The resistance arms are ohms each and the bridge is brought to balance by varying resistance arms, and without the use of any material for the core of either of these coils. The only core in each coil, when bringing to balance, is an air core in each. As used in practice, the ore or mineral may be passed through one arm or coil only of the bridge, this coil being termed the scanner coil. During the time of its passage through the scanner coil, the ore or mineral is thus, in eiiect, absorbing energy from the scanner coil upsetting the balance of the induction bridge, the unbalance current of which is fed to a transformer having a grounded metallic shield between its windings. This shield is necessary to prevent electro-static eiect upon the grids of the ampli- Iier tubes. Plate current from the last amplifier tube is carried through an output transformer which overcomes the bias provided by a bias tube and fires a. gas tube when the bridge is unbalanced by one or other energy-absorptive materials passing through the scanner coil. The gas tube circuit when fired closes a contactor circuit which in turn operates a solenoid-controlled sorter door. The solenoid is controlled by a contactor, the coil circuit of which is controlled by a small relay on the cathode of the gas tube.

In a specific embodiment, however, the method of detection comprises an air core transformer consisting of two coils, hereinafter referred to as balance, or scanner, coils of' 400 turns each of No. 26 magnet wire wound on forms of square, cylindrical or rectangular shape made of a plastic phenolic material, or other 'plastic insulating material, and s connected that the instantaneous fluxes oppose one another. A third coil of the same size and shape, herein termed an exciter coil, is positioned between the scanner coils and is so connected and adjusted between the scanner coils that no output is obtained from the scanner coils when audio power is applied to the exciter coil. The complete three coils are assembled in the aforesaid disposition over a nonmetallic tube o'r conduit through which ore to be versus the frequency of the current on the other, but we do not intend to be limited by such a theory. Some forms of serpentine, for example, respond more strongly than magnetite at suitably chosen frequencies' when the the method of the present invention is used and yet are less magnetic, Hematite responds better than pyrite or galena.v

'I'he use of a balanced bridge circuit has already been disclosed in the prior art. In`the apparatus and method of the present invention, however, the operation is entirely automatic and does not depend upon the visual interpretation of any manifestation. The human element factor is thus completely eliminated in the acceptance or rejection of any particular lump of ore and enters only in adjustment of controls, common to all automatic machines, to obtain the desired performance.

The principal object of the present invention is an improvement in the artof ore or mineral sorted is passed. The output of the scanner coils is fed through a shielded transformer, amplifier and output transformer to the control grid of a gas tube, which when fired develops a high voltage across a resistance and allows power tubes, known as Thyratrons, to iire. The output of the Thyratron power tubes passes to a solenoid coil which operates a sorter door. I't is preferred, however, that the exciter coil, as described in the foregoing specific embodiment of the invention, be wound in two sections, one section being wound with one of the scanner coils and the other section wound with the second scanner coil, the exciter coil having a center tap.

Detection may be had, however, equally well by visiual or audible means. For example, a milliammeter or voltmeter may be used in the output transformer and an unbalanced' reading obtained as metallic ore passes through the scanning coil varying, for exam-ple, with the inductive capacity of the sulphldes in the ore, i. e., varying with the capacity of the sulphides to absorb an appreciablev amount of energy. Alternatively, head phones or a loud speaker may be installed and the unbalance output sensed audibly.

A further alternative means of detection which may be used is a conventional beat frequency generator, the basic frequency of each oscillator being 200,000 cycles. The induction coil of one of these oscillators surrounds a non-metallic tube and. as before, this forms a scanningr coil. Zero beat is obtained with variable condensers in the other oscillator circuit, air being the only medium in the core of both inductance coils. 'When one or other energy-absorptive material is passed through this surrounding coil, the circuit is thrown out of zero beat, the beating frequency varying with the absorbent qualities of the ores or material passing through the scanning coil. For example. chalcopyrite or other non-magnetic metalllcs would give a low beating frequency and magnetic ores would give a high beating frequency. As before, this beating frequency can be used to detect audibly, visually or automatically by using ear phones, indicating meters, or gas tube controlled-sorter doors.

Earlier investigators have determined that materials absorb high-frequency energy in a definite relationship which depends on the dielectric constant of the particular material on the one hand sorting.

A further object of the invention is the provision of an ore sorting method which is easily adjusted to select Various grades of ore or minerals according to their electrical conductivity 0r permeability.

Another object of the invention is to provide an imfproved method involving the separation of Value-bearing minerals from gangues in a highly efficient and economical manner.

A still further object of the invention is to provide an improved method of separating ores, minerals, articles or materials into categories, which depends solely on the electrical energy-absorptive capacity of such minerals, articles or materials.

It is also within the purview of the present invention to provide a machine for attaining the aforesaid objects.

Other objects and advantages of the invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings. in which:

Fig. 1 illustrates diagrammatically the ore feed, the scanning coil, and the electrical circuits;

Fig. 2 is a diagrammatic sectional view of the scanning coil with its electrical balancing and input circuits;

Fig. 3 is a sectional plan View taken on the line 3-3 of Fig. 2;

Fig. 4 is a diagrammatic illustration of thepreferred arrangement of the detector unit, an alternative arrangement of which is shown in section I-A of Fig. l;

Fig. 5 is a vertical sectional View of the assembly of scanner and exciter coils of Fig. 4;

Fig. 6 is a plan sectional view of Fig. 5, taken on the line 6 6 of Fig. 5; and

Fig. 7 is a block diagram of associated circuits.

Fig. 1 is divided into four main sections surrounded by dashed lines and numbered beneath each section as I-a, I-b, l-c and I-d and for circuit of which passes to the exciter coil 4 of the scanning coil assembly. The secondary current of transformer 2 is tapped to obtain a suitable impedance matching with coil 4. This secondary current is fed through shielded cable 3, the outer sheath of which is grounded to prevent electrostatic pick-up. The scanning coil assembly comprises scanning coils 5 and 6 with exciter coil 4 mounted therebetween and inductively coupled therewith, as shown in section I--A of Fig. l. Coils 5 and 6 are also connected in electrical opposition so that normally there is no output from them. Exciter coils 4 and |04 of Fig. 4 and scanning coils 5 and 6 are multiple turn coils each having 400 turns of magnet wire wound on a nonmetallic form made of plastic phenolic material or other insulating material. This mounting is shown in detail in Figs. 2 and 3 for Fig. l, the non-magnetic forms for the scanning coil being designated by the numerals 48 and the form for the exciter coil designated by the numeral 49. Mounting bolts 50, which are threaded throughout their length and which have lock nuts 60 thereon, serve the double purpose of supporting the entire scanning coil assembly on rigid supporting member 5I and providing a means for properly spacing the coils 4, 5 and 6 electrically in relation to each other. An electrostatic grounded shield of non-magnetic foil EI concentrically surrounds the completed scanning coil assembly, as a further protection from electrostatic pick-up. The coils are so spaced on mounting bolts 50 that they are in exact electrical balance with no current or voltage output and lock nuts 60 serve to maintain this proper spacing once it is obtained.

Electrical balance as obtained here in Fig. 1 is by mechanical means, but it is preferably obtained by suitable electrical means in circuit of exciter coil |04 as shown in Fig. 4. In this preferred embodiment shown in Figs. 4, 5 and 6, the exciter coil is shown as |04. The output of transformer 2 passes to variable resistance |02, condenser |05 and condensers |03 which are of a variable capacity type, then to coil |04 through shielded cable 3, the outer sheath of which is grounded. Coil |04 is wound in two sections with a center tap B and coil ends 5-A and E-C, and is so arranged that one section is wound with coil 5 and the other section with coil 6. As stated hereinbefore, the coil l|04 of Fig. 4 is fed from variablev transformer 2 and variable condenser |05 and is thus a tuned circuit. This coil is wound in two sections with one section wound with or adjacent to coil 5 and the other section with coil 6. This arrangement gives a four section scanning coil assembly, the secondaries of which are connected in opposition, with the resistance condenser combination |02I03 serving to correct the voltage and power factor to give an exact electrical balance with no voltage or current output from the secondary coils when no mineral, ore or other material is passing through the tube 40. In the arrangement shown in Fig. 4, the value for resistance |02 would be about 50,000 ohms and the capacity about 500 M. M. F.

Shield cable 3 is a low-loss coaxial type with its capacity xed with varying temperatures. This cable connects the scanning coils to the power source I through the tuning network 2-I05 and zero adjusting network I02-|03. Tube 40, through which ore or minerals to be scanned are passed, is made of rigid non-metallic material, such as horn ber, and is concentrically surrounded by forrns 48, 49, carrying coils 4, 5 and 5 or |04, 5 and 6. No mechanical connection exists between tube 40 and coil forms 48, 49, this tube 40 serving primarily to protect these forms and the coils carried thereon from mechanical damage from falling mineral lumps 4|. Mounting bolts 50 are located outside the coils 4, 5 and 6 as shown in Figs. 2, 3, 5 and 6 which also show the positioning of tube 40 in relation to these coils. As shown, the bolts 50 are carried by the rigid member 5I and are disposed outwardly from the coils and coil forms. This disposition is necessary so that magnetic flux, caused by the exciter coil, does not pass through the bolts. By this disposition of bolts 50 and by the proper use of lock nuts G0, the exact electrical balance hereinbefore described is maintained by mechanical means.

As heretofore stated, it is preferred that this exact electrical balance be obtained by the electrical means shown in Fig. 4 and hereinbefore described, but it will be apparent that either the electrical or mechanical means may be used to obtain and to maintain this exact electrical balance. This exact electrical balance, with no current or voltage output from the coils and with no ore or mineral passing through tube 40, is extremely important in obtaining proper functioning of the equipment. Transformer 'l receives the unbalance current from coils 5, 6, when ore or mineral passes through tube 40 and delivers the current, through low-loss shielded cable 8, to transformer 9, the secondary of which feeds to potentiometer I0 and to the contro1 grid of amplier tube II. As the amplifier is widely separated from its scanner and electrostatic pickup, and magnetic induction from ejector coil 31 may be severe, a high-pass iilter I2, cut off frequency 1000 C. P. S., is interposed between tube II and tube I3. The audio impulse from ampliler tube |I passes to high pass filter I2 and to output tube I3. Tubes II and I3 are supplied with plate current from a common D. C. supply here shown as battery I9. provide the necessary self-bias with no signal output for tubes |I and I3 and condensers associated with resistors I4 provide a path for audio power. The plate current from tube I3 passes through transformer I5 to A. C. voltmeter I6 and to the control grid of tube 20. A switch Il is provided with voltmeter I6 so that a reading of unbalance current from coils 5 and 6 may be obtained with voltmeter I6 and so that a minimum reading with a maximum sensitivity adjustment of potentiometer i0 may be obtained. Since electrostatic pick-up cannot be Wholly eliminated, some reading will always be obtained but adjustment of coils 5 and (i4 or of resistorcondenser I02|03 is made to maintainr this reading at a minimum gure without mineral or any foreign metallic piece in tube 40. Certain minerals or gangue will give a certain reading and voltmeter I 6, in conjunction with potentiometer I0, may also be used as a sensitivity indicator by placing a, lump of ore manually in tube 40, after obtaining the aforesaid minimum reading without ore or foreign material, and using the reading thus obtained as a reference reading. Tube v2|] is a gas tube or thyratron, such as R. C. A. 2050, and is supplied with D. C. as from battery 22 or other constant voltage D. C. source. When the control grid of tube 20 receives a signal pulse from scanning coils 5, 6, through transformer I5 and resistor I8, it fires and continues to re until the plate current from the D. C. supply is interrupted as hereinafter described.

Cathode resistors |4 asomar 7 The continued ming of the tube 20 is an important feature of the present invention since it provides a means for lengthening the duration of the signal pulse from scanning coils and 5 which in turn provides a means for lengthening the duration of current passage through solenoid coil 31 which signal pulse -would normally be insufcien'tly long to permit the ejector mechanism 44 to complete its full stroke. The circuit for tube 20 isswitch 2|, battery 22, or other source of D. C. supply and resistance 23. D. C. voltmeter 32- and switch 33 provide an indication for setting of potentiometer 23. The switch 2l may be replaced and in practice preferably is replaced by a timing relay. ,The tubes 28, 29, through which operation of the solenoid coil 31 and the ejector mechanism 44 are operated, are gas-nlled power tubes and those used in the present instance are known as Thyratrons type 57. These tubes are supplied with power from line voltage on a 550 volt 25 cycle single phase circuit through power transformer 34 and they ordinarily would stop conducting as soon as the pulse from the detector has passed. Thus, when tube 20 res, a high voltage is developed across resistance 26 due to the current ow therethrough and this voltage overcomes the normal bias voltage 25, allowing tubes 28, 29 to re. Since the tube 20 continues firing with the uninterrupted D. C. supplied thereto, this overcome bias voltage 25 allows tubes 2829 to continue ring and pass D. C. through solenoid coil 31 and the associated circuit. Coil 31, however, is composed of many turns of wire of high inductance and the D.- C. through it cannot build upinstantly.

The voltage across resistance 3i thus reaches its' full value some time after bias voltage 25 has been removed by tube 20 and resistor 26. The lengthened duration of the signal pulse from scanning coils 5 and 6 is thus attained since the positive voltage obtained from resistor 3|, due to tube current 29, 29 passing through it, is applied in the reverse direction to tube 20 and resistor 25 thus stopping it conducting by placing a high negative bias or voltage to the plate of tube 20 and allowing the grid of tube 20 to regain control from normal bias circuit battery 25, potentiometer 23, transformer l5 and resistor i8. Resistance 3i is a potentiometer, the adjustable arm of which can be set to control the timing ejector mechanism strokes.

In the ore stream being fed to the scanner coils there would be high grade, low grade and tailings. A high grade lump will inuence scanner coil circuit i4- 5, 6, in its free fall from 39 through 40 sooner than a low grade piece and would cause ejector plate 44 to take its forward pdsition too soon. Some control of ejector time is necessary for this-condition and it is obtained by adjusting potentiometer 3l for best over-all.

operating condition. Thus, gas tube 20 stops conducting by forcing its plate electrically negative from the circuit it initiated. Resistor 23 is a potentiometer with a manually operated knob by which a proper adjustment of bias-voltage may be applied to tube 20 to prevent faulty firing from normal noise level through the amplifier. .Potentiometer 23 is also used in conjunction with potentiometer I0 to provide Athe sensitivity required for separating various grades of mineral or for sorting barren rock from. value-bearing mineralsuitable for milling and smelting. Potentiometer 24 also has a manually operated knob so that the proper bias may be applied to tubes 28, 29 preventing them from ring incorrectly through line voltage variations across power transformer 34. As heretofore stated, the line voltage in the present instance is 550 volts, 25 cycle single phase. Potentiometer 24 is adjusted for correct bias by using a portable meter or indicator and no further setting of 24 is necessary. Resistance 21 is a limiting device to prevent excessive ow of current between 25 and the circuit of which resistor 3l forms a part. The output of tubes 28, 29 passes to the resistor 3|, solenoid coil 31 and switch 35, returning to power transformer 34. While 35 is here shown as a switch, it is preferred to use a timing relay A in practice. Ejector plate 44 is urged forward very rapidly when solenoid coil3 is energized and is returned to the inoperative position shown in the drawing by return spring 45 when coil 31 is de-energized.A Condenser 36 assists in returning the ejector plate to at rest" position by absorbing induced voltage across coil 31. Ejector plate 44 is rigidly attached to one end of a nonmetallic rod 55 which may be of a plastic phenolic material or other insulating material and this non-metallic rod 55 is attached at its opposite Aend to the forward end of steel plunger 45 which has one end of return spring 4S attached through steel extension rod 56 to its opposite end. The other end of return spring 4S is secured to solid mounting 41. Rods 56, 55 are-carried in bearings 51, thus controllingthe directional path of movement of these rods and of plungerV 45 and of ejector plate 44. As will be seen in the drawing, this path of movement is diametrically across the path of flow of ore lumps passing through the scanner coil assembly. Bin separator 43 is also disposed in the ore lump ow path beyond the transverse path of movement of plunger 45. This bin separator 43 is preferably off-set in the ore lump ow path so that all ore passing through tube 40 follows along to path 59 when the plunger 45 is deenergized and elector plate 44 is in the at rest or at home position shown in the drawing. Plunger 45 is located within the solenoid coil 31 and when the latter is energized by current passing through it as heretofore described, plunger 45 and ejector plate 44 are urged forward across the ore iiow path thereby closing on path 59 and diverting the ore lump into path 58. Since the flow of current through coil 31 is initiated by the electrical energy-absorptive capacityof the ore lumps passing through tube 40 and by the effect on the scanner coil assembly of that electrical energyabsorptive capacity, it will be apparent that barren rock or other material having negligible or no capacity for energy absorption will not initiate the current flow, and ejector plate 4,4 will remain in the at rest position and the ore lump will continue in path 59. When ore or mineral having an electrical energy-absorptive capacity suilicient to effect the electrical balance of the scanner coil assembly passes through tube 40, a ilow of current is initiated by coils 5 and 5 through the amplier unit, the bias supply and the output circuit, thus initiating the mechanical functioning of the detector unitv by moving ejector plate 44 into the ore ow path. As more fully described hereinbefore, means are provided for prolonging the impulses operating vejector plate 44 to maintain it in operative position for diverting ythe electrical energy-absorptive ore lump into values-ore-iiow path 58. This feature of prolonging the duration of impulses is important in its eifect on the speed of ore handling which, with the machine described, may be 3 to 4 ore lumps per second of 2 to 4 pounds weight each. It will be apparent, however. that the volume of feed and the capacity to handle lumps of other size and weight than those given may be varied within wide limits by appropriate alterations in design of the equipment. For example, the number of pieces handled per second could be increased for smaller pieces with appropriate changes in the mechanical design or, in the case of larger lumps, less Apieces per second could be handled with a correspondingly more rugged mechanical design. The size of tube 40 and of the scanner coils surrounding this tube would naturally be appreciably increased for larger lumps and such a unit would be equally eicient for handling smaller lumps. It is an essential feature of the present invention, however, when the circuits of the present invention are used to operate ejector plate 44 or similar mechanical sorter as well as being used as a means for detecting electrical energy-absorptive capacity in passing ores or material, that two pieces of ore or mineral should not pass through tube l0 within the zone where their energy-absorptive capacity would affect the electrical balance of the scanner coils at the one time and the volume of feed (i. e.,

the number of pieces handled per minute) must,

specification is intended in a mutually comple.

mentary manner and that generally these terms are essentially interchangeable. It wil be apparent, for example, in sorting ore, that if the sensitivity is sufciently high to detect any appreciable values in the ore lumps, the tailings will be particularly clean (i. e., selective) and that, conversely, if the sensitivity is relatively low onlyv high grade lumps will be recovered, in which case the concentrate will be selective. Thus, any adjustment of either the sensitivity or the selectivity will have at least a proportionate eect on the other. Since it has been established that each mineral species has an individual frequency range to which it responds best, this dual adjustability of sensitivity and selectivity makes the therefore, be maintained within that limitation.

As will be noted hereinafter however, the onepiece-at-a-time presentation to the scanner coil is not essential when the unit is used solely for detecting the change in tenor of an ore stream or for similar purposes. The mineral or ore feed mechanism includes means for maintaining the one-piece-at-a-time feed volume and may be described as follows:

Mineral or ore ows from the bin 53 onto feedy roll belt 42 or to other appropriate means for feeding ore lumps in single appropriately spaced lumps or units to the tube 40. In the present instance, the feed roll belt 42, driven at an appropriate speed, feeds the ore lumps to trough 39 which is inclined toward the tube 40 and which is preferably equipped with vibrating means 38 which imparts a longitudinal vibration 52 to the trough 39. This vibration is necessary not only to keep mineral lumps 4l sliding down trough 39 but also to so space them in the trough that they will be discharged singly into the tube 40 and thus will fall through the tube 40 one at a time. Longitudinal vibration may be obtained by a simple electrically operated device, by a mechanical cam operated device or by a combination of these methods. If the ore lump is barren, it will deiiect in barren or path 59 since deflector plate 44 will remain in the at rest or home position shown in Fig. 1. If the ore lump is of a grade for selecting, however, it will unbalance scanner coils 5, 6 and an impulse will be carried through the amplifier and associatedcircuits to solenoid coil 31 which will cause plunger and ejector plate 44 to move forward with the latter closing off the barren-ore-ow path 59 and diverting the ore lump into values-ore-flow path 58. After passage of the values-bearing ore lump through tube 40, the solenoid coil 31 will be deenergized in Athe manner heretofore described and the plunger 45 and ejector plate 4'4 will be returned to the inoperative or at rest position by the action of return spring 46.

The field for application of the process of our invention is extensive. It may be stated that eddy current losses increase with frequency and thus non-magnetic sulfides are more readily detected with an increase in frequency. Sensitivity field of application for the present invention a very extensive one. For example, since many minerals have dilerent inductivev capacities 'or absorbent qualities, it is thus possible by the method of our invention to separate ores of high and low inductive capacity from each other as well as from gangues, in which case the ores preferably would be passed through two machines in series. The first of these machines would be adjusted to reject all the gangue and to retain all responsive components and pass them to the second machine which would be so adjusted as to separate the highly responsive and the poorly responsive materials from each other by retaining the one and rejecting the other. Similarly, the present invention may be used in many cases for instantaneous detection of a change in the tenor of an ore, pulp stream, or other metallurgical product, at a saving in time and cost as compared with ordinary analytical procedures. It is particularly adaptable for detecting tramp iron, including non-magnetic manganese steel in an ore stream which does not contain responsive materials, for example, molybdenum ores. It will be apparent that when the mechanism of the present invention is used in connection with an ore stream forthe purpose of detecting a change in tenor of the ore stream or for the purpose of detecting the presence of tramp iron, non-magnetic manganese steel or non-responsive materials such'as molybdenum ores, the one-piece-ata time presentation to the scanner coil need not be followed. It will be obvious that this onepiece-at-a-time presentation to the scanner coil is required only when sorting as well as detection is desired. It is thus also apparent that the method of our invention is capable of widespread use, particularly within the mining and metallurgical Generally, the sensitivity of the present method will increase with an increase in frequency. We, therefore, do not intend to be limited to any frequency and we may use frequencies through the audible range and as high as the megacycles range. Y

We have stated above that the method of our invention is particularly applicable within the mining and metallurgical arts. At a frequency of 200,000 cycles used with a beat frequency generator, the following minerals were found responsive; magnetic pyrrhotite, non-magnetic tests covered by the sorter frcm'the magnet reject material in the form of a concentrate averaging:

Composition: Per cent Copper 1.85 Nickel 3.12 Sulfur 24.5 Pyrrhotite 50.1 Silica 17.7

The silica assay of 17.7% was thus well below the limit and the weight recovery of 16.1% amounts to approximately the same tonnage as 'Average of five tests on open pit lump ore Assays Per Cent Distribution Weight Avg. Wt. A Product Lbs Lbs Pe f Pelbflxet Perlgem Pergeni Ptrfycrrej Figi weight copper Nickel sulfur Pyn. Rock 2. 1.23 1.42 13.5 28.1 04.4 09.2 88.0 94.9 97.1 08.4 59.4 l ggg 2:22 0. 03 0.20 1.5 1.7 95.0 17.0 11.1 4.4 2.9 1.5 21.8 'rail 215 2. a0 0. 05 0. 07 0. 2 0. 1 99. 5 13. 8 0. 9 0. 7 0. 1 0. 1 18. 8 one. Feed-.. 1. 550 2. 01 0.90 1.03 9,0 19.0 74.7 100.0 100.0 00.0 100.0 100.0 100.0 M1dd.+'rai1- 479 2.30 0.97 0.17 0.9 1.0 97.4 30.8 12.0 5.1 29 y 1.0 40.0

Average of three tests on underground lump ore Assays Per Cent Distribution Weigbt, Avg. Wt., V Product Lbs. Lbs. Pc. l Pe'bent PerNient Pergent Pfygleflt Pelont Weight Copper Nickel Sulfur Pyrr. Rock 189 1.2 0.05 1.97 14.4 31.7 02.0 40.7 70.4 80.8 82.4 83.2 81.4 0.8 0.31 0.39 3.9 8.9 89.8 28.1 23.2 15.9 15.3 15.0 81.0 .Tail 09 0.7 0.078 0.074 0.5 0.9 97.7 31.2 v 0.4 3.3 2.3 1.8 97.0 Calc. Feed. 220 0. 9 0. 37 0. 70 v 2 15. 7 81. 0 100. 0 100.0 100. 0 100. 0 100. 0 100. 0

M100-T011 190 0. 7 0. '19 0. 22 2. 1 4. 3 94. 0 59. a' 29. 0 19. 2 17. 0 10. s 08. 0

In the above tests the frequency generator was xed at 1500 cycles per second. A setting of v maximum sensitivity was maintained during the tests in order to make a tailing as low in sulfide as possible. This tailing was inal. In each test, the rougher concentrate obtained was put through the selector a second time at a lower sensitivity rating, the reject from this second passage being classed as middlings.

Since the middling for the open pit tests averaged only 0.26% nickel which might not be of suflicient grade to warrant milling, a line is in cluded to show the total reject if middling were discarded with tailing. I

Actual comparison of the ore sorter of the present invention was made in the following manner with a magnetic sorter such as is commonly used.

It has been a commonpractice for many years to scalp out a concentrate of high grade, suitable for use as blast furnace feed, by the use of magnetic pulleys. The silica content of such blast furnace feed must be under 20%. The ore sorter of the present invention was set up to operate on the rejects from the magnetic pulleys to see if any high grade material could be recovered 05 which had failed of recovery on the magnets. The magnets continued to operate ahead of the sorter and the results obtained, which are given below, indicate the exceptionally good results which are obtained by the methods of the present invention. These results are the average of 15 tests, each test involving approximately 1000 pounds of ore in pieces averaging 6 inches diameter and weighing about 4.8 pounds each. A recovery of 16.1% of the feed weight was re- 7 the magnets were recovering from the ore before it reached the sorter. The average grade of the magnetic concentrate was:

Per cent Composition:

Copper 2.50 Nickel 2.88

Sulfur 23.1 Silica 19.0

terial yso recovered was actually higher grade than that recovered by the magnetic sorter.

It is to be observed from the foregoing that the method of the present invention and the means for putting that method into practice provide a highly eiilcient and economical method for sorting ores and minerals. It will be apparent that this method is not limited by either the specific gravity or the magnetic properties of the ore or minerals being handled and that no coincident handling and/or removal or recovery of Water or other fluid is required.

Although the present invention nhas been de'- scribed in conjunction with preferred embodiments, it is to be observed that modifications and variations may be resorted to, as one skilled in the art will readily understand. Thus, other means for feeding ores or minerals to the detector unit may be used and other methods of scanning coil balancing and of associated electrical circuits may 13 be used. Various methods of electing ore or gangue, different types of scanner coils, including phototube detection, and of associated electrical currents may be used.

We claim:

1. In an apparatus for detecting the presence of metal values in materials such as ores, a detector unit comprising a pair of scanner coils connected in electrical opposition and an exciter coil therebetween, said exciter coil being in two sections and having a center tap, each of said sections being wound with the scanner coil adjacent thereto, said coils being axially aligned to form an air core transformer adapted for passage of ores therethrough, means for energizing said exciter coil comprising a source of audio power and including a variable resistance and variable capacity condensers whereby exact electrical balance devoid of voltage and current output from the secondary coils is obtained, but adapted to unbalance on passage through said unit of electrical-energy-absorptive material, means for passing said absorptive material through said unit, an amplier tube and means for feeding the unbalance current created by said passage to said amplifier tube, said feeding means including a rst transformer and a second transformer and the secondary circuit of said second transformer, each of said transformers having an electrostatic shield between its primary and secondary windings, an output tube, means for passing the audio impulse of said amplifier tube to said output tube including a coupling condenser, a battery for supplying said amplifier tube and said output tube with plate current, a gas tube and a battery for supplying direct current to said gas tube, means for passing output plate current of said output tube to the grid of said gas tube, said passing means including a transformer and a resistor whereby firing of the grid of said gas tube is initiated, a pair of power tubes and a source of power for said power tubes including a transformer, means intermediate said gas tube and said power tubes for overcoming the normal bias voltage and thereby prolonging the ring of said power tubes, said intermediate means comprising a resistance element adapted for developing a high voltage with the passage of output from said gas tube, a multi-tum high inductance solenoid coil connected to be energized by the direct current emitted by said power tubes during said firing, an adjustable resistor associated with said power tubes and said solenoid whereby positive voltage is built up during said energization and is ultimately applied in a. direction reverse to the direction of said impulses to the plates oi' said gas tube thereby interrupting the tiring of said gas and power tubes.

2. In an apparatus for detecting the presence of material having a capacity for absorption of electrical energy comprising in combination an electrically-insulating channel member for passing materials therethrough, a multiple coil detector unit encircling said channel member and substantially coaxial therewith, said detector unit comprising at least a pairv of scanner coils connected in electrical opposition, and at least one exciter coil interposed between said scanner coils transformer and means for applying the secondary circuit of said transformer to said exciter coil, a gas tube circuit adapted to re on passage therethrough of unbalance current impulses created by passage through said channel member of materials possessing said energy-absorptive capacity, an output circuit including at least one power tube having "ts grid connected in the gas tube circuit and having its plate connected to an external power supply source, a high impedance coil connected in the output circuit and said output circuit being connected to the gas tube circuit through a potentiometer for applying a high negative voltage to the plate ofthe gas tube for the blocking of said tube in timing relation responsive to the output circuit voltage.

3. An apparatus for sorting ores containing metal values susceptible to absorption of electrical energy from ores devoid of said values comprising in combination an air core transformer consisting of a pair of scanner coils connected in electrical opposition and at least one exciter coil coupled therewith, means for energizing said exciter coil, means for adjusting the energizing of the exciter coil whereby effective output current and inductively coupled therewith, means for supporting said coils and means for so adjusting said 70 exciter coil with said scanner coils that output is obtained from said scanner coils on application impulses are obtained from said scanner coils only during passage through said air core transformer of material of a given energy absorptive capacity, means for directing the material to pass through the transformer, means for amplifying the output current impulses from the scannerv coils, a thyratron connected to be grid controlled by the amplified current impulses, means for applying a normal bias to the thyratron circuit, an output circuit including at least one power tube and a high impedance solenoid coil, an external power source for the output circuit and said thyratron circuit having connection to the output circuit through a potentiometer to eiect negative biasing of the thyratron plate responsive to the energizing of the solenoid coil and to overcome the normal biasing of the thyratron electrodes to effect a delayed action blocking thereof.

ERNEST HERBERT ROSE. ARTHUR ERNEST PRINCE.

REFERENCES CITED The following references are of record in the ille of this patent:

OTHER REFERENCES Radio World, Dec. 1936. pages 50 to 56. 

